Non-circular electrical cable having a reduced pulling force

ABSTRACT

In various embodiments, a non-circular electrical cable having a reduced pulling force attributable to the exterior surface of an outer sheath, and method of producing the same is provided. In various embodiments, an outer sheath of the cable may comprise a first and second sheath layer, the second sheath layer being located external to the first sheath layer, and comprising a nylon material configured to reduce the pulling force necessary for installing the cable. In various embodiments, the first sheath layer may be extruded using a tube extrusion method into a substantially circular shape, and the second sheath layer may be extruded using a pressure extrusion methods onto the exterior surface of the first sheath layer while maintaining the at least substantially circular shape of the sheath. The sheath may then be pulled onto the surface of a plurality of conductors to form the non-circular electrical cable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to application Ser. No. 14/620,963,filed Feb. 12, 2015; the contents of which are hereby incorporated byreference in their entirety.

BACKGROUND

Non-metallic sheathed cable, such as NM-B type cable, is often used forproviding electrical systems within residential structures. Knownnon-metallic sheathed cable assemblies often comprise one or moreelectrical conductors individually coated in an electrical insulator(e.g., a solid or stranded copper wire coated in a plastic material)bundled together and collectively sheathed in a non-metallic outersheath. Generally the non-metallic outer sheath comprises anon-conductive polymer such as poly-vinyl chloride (PVC) and has beenunderstood to provide mechanical protection for the bundled wiresagainst insulation tears and abrasion.

During installation, these cables often must be threaded through aseries of rough-hewn holes cut through wooden floor and ceiling joists,headers, and wall studs (such as those commonly referred to as 2×4s,2×6s, 2×8s, and/or the like) or through narrow plastic conduit. Due totime pressures involved in installing electrical cable and the oftencomplex shapes of walls and structures included in residentialbuildings, the electrical cable installation path comprises asubstantially non-linear path through multiple wooden studs. These cableinstallation paths often run substantially horizontally through a seriesof wooden wall studs, turn around corners to follow additional pathsegments substantially perpendicular to previous segments, and turnvertically to run along the length of wooden wall studs to electricaloutlets, wall mounted switches, or ceiling mounted light sources.

The exterior surfaces of the non-metallic sheathed cables often have ahigh dynamic coefficient of friction, and therefore installation ofthese cables along the installation path may require a substantial pullforce to overcome the frictional force occurring between thenon-metallic sheathed cable and the surfaces of the installation pathwhile the cable is being pulled. In some installations, the pullingforce necessary to move the cable through the installation path may behigh enough to deform or tear the outer non-metallic sheath. Therefore,when installing long segments of non-metallic sheathed cable, multipleinstallers may be necessary to thread the non-metallic sheathed cablealong the installation path. A first installer may be necessary to pushlengths of cable into the installation path, and one or more additionalinstallers may be necessary to pull the provided lengths of cable alongthe installation path.

Electricians and installers have previously coated non-metallic sheathedcables with a separate cable lubricant, often in the form of a liquid orgel, at the installation site to reduce the coefficient of friction ofnon-metallic sheathed cables. Applying these separate cable lubricantsat the job site may require additional installation time, can be messy,and, depending on the chemical composition of the lubricant, maynegatively impact the mechanical and insulative properties of thenon-metallic sheath.

As noted in U.S. Pat. No. 7,411,129 to Kummer et al., incorporatedherein by reference, and patents and patent applications relatedthereto, advances have been made in decreasing the pulling forcenecessary to install electrical conductors in substantially non-linearinstallation paths. These advances include sheath formulations whereinnylon or another polymer is mixed with a lubricant and formed over theoutside of the conductor in order to decrease the surface coefficient offriction. However, these efforts have been directed to generallycircular conductors, such as circular Thermoplastic High Heat ResistantNylon (THHN) wiring or the like.

In many residential installations, however, substantially flat ornon-circular cables, such as Southwire's Romex® 14/2, 12/2, or 10/2cable, are used for a substantial portion of electrical wiring. Suchcable may comprise two separately insulated conductors and a separateground wire arranged in a substantially flat arrangement (e.g., thecenter point of each of the three wires are nominally aligned in asingle plane). The three wires are encapsulated in a non-metallic outersheath as described above. As noted herein, previous attempts todecrease the pulling force necessary for installation of non-metallicsheathed cables have been limited to circular wires and cables. Physicalcharacteristics of the materials utilized in the reduction of thesurface coefficient of friction for non-metallic sheathed cables havepreviously limited the commercial manufacture of previously knownmethods and materials to circular cables and wires. Moreover, productsafety and certification organizations, such as the UnderwritersLaboratory (UL), have implemented sheath thickness and uniformitystandards for non-metallic sheathed cables, highlighting the importanceof a uniform sheath thickness. Therefore, new manufacturing methods areneeded to consistently produce non-circular, non-metallic sheathed cablewith a reduced surface coefficient of friction in order to decrease thepull force necessary to install these cables in generally non-linearcable installation paths.

BRIEF SUMMARY

Various embodiments of the present invention are directed to a processfor producing non-circular electrical cable, wherein the non-circularelectrical cable comprises one or more conductors arranged in anon-circular arrangement and an exterior sheath comprising a firstsheath layer and a second sheath layer. A process according to variousembodiments of the present invention comprises steps for: (1) advancingconductors through an extruder head, (2) extruding a first sheath layercomprising a plastic material around the conductors, wherein the firstsheath layer is initially extruded in a substantially circular shapehaving an inner surface and an exterior surface and at least a portionof the inner surface thereof is spaced from the conductors, (3)extruding a second sheath layer comprising a nylon material onto theexterior surface of the first sheath layer, (4) applying a negativepressure to the interior surface of the first sheath layer, therebypulling the first sheath layer and second sheath layer onto theconductors and into a non-circular shape having a cross sectionsubstantially similar to the combined cross section of the one or moreconductors, and (5) cooling the first and second sheath layers. Invarious embodiments, the second sheath layer may additionally comprise alubricant for decreasing the pull force of the cable.

In addition, various embodiments of the present invention are directedto a non-circular electrical cable comprising one or more conductorsarranged in a non-circular arrangement and an exterior sheath looselysurrounding the conductors having a non-circular cross-section, theexterior sheath comprising a first sheath layer and a second sheathlayer. In various embodiments, the first sheath layer has an exteriorsurface and an interior surface, and comprises a plastic material. Invarious embodiments, the second sheath layer may have an exteriorsurface and an interior surface, and comprises a polyamide, such as anylon material. Additionally, the second sheath layer may comprise alubricant for decreasing the pull force of the cable.

Yet other embodiments of the present invention are directed to anon-circular electrical cable comprising one or more conductors arrangedin a non-circular arrangement and an exterior sheath loosely surroundingthe conductors having a non-circular cross-section, the exterior sheathcomprising a first sheath layer and a second sheath layer. In variousembodiments, the first sheath layer has an exterior surface and aninterior surface, and comprises a plastic material. In variousembodiments, the second sheath layer may have an exterior surface and aninterior surface, and comprises a polyolefin (e.g., polypropylene).Additionally, the second sheath layer may comprise a lubricant fordecreasing the pull force of the cable.

Yet other embodiments of the present invention are directed to anon-circular electrical cable comprising one or more conductors arrangedin a non-circular arrangement and an exterior sheath loosely surroundingthe conductors having a non-circular cross-section, the exterior sheathcomprising a first sheath layer and a second sheath layer. In variousembodiments, the first sheath layer has an exterior surface and aninterior surface, and comprises a plastic material. In variousembodiments, the second sheath layer may have an exterior surface and aninterior surface, and comprises a polyester. Additionally, the secondsheath layer may comprise a lubricant for decreasing the pull force ofthe cable.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 shows an exemplary schematic of a system utilized to producenon-metallic sheathed cable according to one embodiment of the presentinvention;

FIG. 2 shows an exemplary schematic of various components present withinan extruder head, according to one embodiment of the present invention;

FIGS. 2A-A and 2B-B show exemplary cross sectional views of a sheathedcable at various points during the manufacturing process, according toone embodiment of the present invention;

FIG. 3 shows a cutaway view of a sheathed cable according to oneembodiment of the present invention;

FIGS. 4A and 4B show components of a pull force test apparatus accordingto various embodiments of the present invention; and

FIG. 4C illustrates a threading pattern for threading a cable to betested using the testing apparatus according to various embodiments ofthe present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, the invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

Referring initially to FIG. 1, there is depicted a schematic diagram ofexemplary equipment 1 utilized to produce an electrical cable accordingto one embodiment of the present invention, usable equipment isdescribed in co-pending U.S. patent application Ser. No. 14/620,963,filed on Feb. 12, 2015, the entire contents of which is incorporatedherein by reference in its entirety. As shown in FIG. 1, multipleconductors 2 a, 2 b, 2 c may be combined to create a multi-conductorcable. In various embodiments, the conductors may comprise multipleinsulated conductors 2 a, 2 c and one bare conductor 2 b. For example,various embodiments may comprise two 12-gauge insulated conductors andone 12-gauge bare ground wire and may be commonly referred to as “12/2wire.” Each insulated conductor may comprise a conductive elementsurrounded by an insulating material. The insulating material may, incertain embodiments, comprise an extruded polymer material such as PVC,a nylon material, and/or other materials having electrical insulativeproperties. In various embodiments, the PVC may be a foamed PVC materialor a re-grind PVC material obtained from recycled PVC products. Althoughillustrated as comprising three conductors, it will be understood bythose skilled in the art that any number of conductors may be utilizedherein.

Referring again to FIG. 1, the multiple conductors 2 a, 2 b, 2 c may, invarious embodiments, be stored using wire storage devices illustrated inFIG. 1 as a plurality of spools 3 a, 3 b, 3 c. It will be understood bythose skilled in the art that any of a variety of wire storage devicesmay be utilized, including cages, barrels, pallets, and/or the like. Themultiple conductors 2 a, 2 b, 2 c may be removed from the wire storagedevices during the electrical cable production process as needed, andsupplied to an extrusion head 4 during production. Although not shown inFIG. 1, dam paper 28 and/or a paper barrier 29 may also be supplied tothe extrusion head 4 in various embodiments. The equipment mayadditionally include a polyamide-supply tank 5 containing a polyamide 6(e.g., nylon) used to form a second sheath layer 26 of a resulting cable13 having a reduced pull force. As illustrated in FIG. 1, the polyamide6 is illustrated as a plurality of polyamide pellets, however otherpolyamide forms may be utilized. The polyamide 6 may be supplied to theextruder head 4 during production via a polyamide-supply conduit 7. Invarious embodiments, the equipment may additionally include anadditive-supply tank 8 containing an additive composition 9 (e.g., afire retardant and/or a lubricant) that may be combined and mixed withthe polyamide 6 prior to supplying the resulting mixture to theproduction process. As a non-limiting example, the additive composition9 may comprise a lubricant, such as erucamide, a silicon-based material(e.g., a silicon oil), and/or the like configured to further reduce thepull force of the cable attributable to the resulting second sheathlayer 26. In various embodiments, the additive composition 9 may besupplied to the polyamide-supply tank 5 where it is mixed with thepolyamide 6 to create a substantially homogenous mixture of polyamideand additive composition via an additive-supply conduit 10. The additivecomposition 9 also, or alternatively, may be supplied directly to theextruder head 4, where it may be combined with the polyamide 6 prior toand/or during an extrusion process. In such a configuration, an extruder(e.g., a twin-screw extruder, not shown) is provided just upstream ofthe extrusion head 4 and is configured to pressurize, heat, and combinethe polyamide 6 and additive 9 in a molten state prior to extruding thecombined material. The polyamide 6 and additive 9 may be provided to theextruder in pellet form or molten form.

The equipment 1 may additionally include an insulator-supply tank 11containing an insulator material 12 configured to supply the insulatormaterial 12 to the extruder head 4 via an insulator-supply conduit 11 a.In various embodiments, the insulator material 12 may comprise a plasticmaterial having electrical insulative properties, such as PVC, and maybe supplied to the extruder in pelletized form or in a molten state. Invarious embodiments, at least a portion of the PVC may be a re-grind PVCmaterial obtained from recycled PVC products. As illustrated in FIG. 1,the insulator material 12 may be stored in the insulator-supply tank 11as a plurality of insulator pellets, however the insulator material 12may be stored in a variety of forms. In various embodiments, theinsulator material 12 may be supplied to the extruder head 4 at alocation upstream from the polyamide 6 supply location via theinsulator-supply conduit 11 a. In various embodiments, the insulatorsupply conduit 11 a may comprise an extruder (e.g., a single-screwextruder, not shown) configured to pressurize and heat the insulatormaterial 12 prior to supplying the insulator material to the extruderhead 4. The insulator material 12 may also, or alternatively, be foamedas part of the extrusion process, such that the overall density of theinsulator material is reduced. As will be described in greater detailherein, the polyamide 6, additive composition 9, and insulator material12 may be applied to the conductors in the extruder head 4, such thatthe resulting cable 13 comprises the multiple conductors 2 a, 2 b, 2 c,surrounded by a multi-layer sheath having at least a first sheath layer27 comprising the insulator material 12 and a second sheath layer 26that may comprise the composition of polyamide 6 and additive 9. Withthe additive 9, the exterior surface of the resulting cable 13 comprisesthe second sheath layer 26 which results in a cable having a reducedpull force relative to the prior art, thus reducing the pulling forcenecessary for installing the cable 13 in an installation location.

In various embodiments, the equipment 1 may comprise a cooling box 14containing a cooling fluid 15. The resulting cable 13 may be fed intothe cooling box 14, in order to cool the extruded materials included inthe resulting cable 13. The cooling fluid 15 may comprise water,although a variety of alternative cooling fluids may be utilized. Thecooled cable 16 may be fed to a cable take-up 17, such as a spool, cage,barrel, and/or the like for transfer and storage. As will be describedin greater detail herein, many modifications and other embodiments maybe provided according to the terms of this invention. As a non-limitingexample, the production process may omit the additive composition 9entirely, and therefore the equipment 1 may not include theadditive-supply tank 8 and additive-supply conduit 10. In variousembodiments, the equipment 1 may omit the additive supply tank 8, andthe additive composition 9 may be dispersed throughout the polyamide 6,such as a plurality of separate additive composition pellets mixed withthe polyamide pellets, or in a plurality of combined pellets, eachcomprising both polyamide 6 and additive composition 9.

In various embodiments, the polyamide-supply tank 5 may be embodied as apolyolefin-supply tank containing a polyolefin material (e.g., apolypropylene material). In yet other embodiments, the polyamide-supplytank 5 may be embodied as a polyester-supply tank containing a polyestermaterial. In such embodiments, the processing steps described herein inreference to the polyamide-supply tank 5 and polyamide 6 may beperformed utilizing the polyolefin-supply tank and polyolefin and/orutilizing the polyester-supply tank and polyester. In such embodiments,the second sheath layer 26 of the resulting cable 13 comprises apolyolefin material and/or a polyester material.

As noted, the polyamide-supply conduit 7 may comprise an extruderassembly (e.g., a twin screw extruder or single screw extruder)configured to heat and supply molten polyamide 6 to the extruder head 4.Similarly, the insulator material supply conduit 11 a may comprise anextruder assembly (e.g., a twin screw extruder or single screw extruder)configured to heat and supply molten insulator material 12 to theextruder head 4.

Extruder Head

Referring now to FIG. 2, the extruder head 4 may comprise a plurality ofindividual components each configured to facilitate the extrusion of thefirst sheath layer 27 and second sheath layer 26 onto the multipleconductors 2 a, 2 b, 2 c. In various embodiments, the extruder head 4may comprise a tip holder 18 having a guide channel 19 extendingtherethrough. In various embodiments, the guide channel 19 may be sizedand shaped such that the multiple conductors 2 a, 2 b, 2 c maintain apredefined orientation as the multiple conductors 2 a, 2 b, 2 c arepassed through the extruder head 4. As a non-limiting example, the guidechannel 19 may be in a substantially stadium or flat oval shape suchthat the multiple conductors 2 a, 2 b, 2 c each having a round profileand maintain a nominally flat orientation, such that the center pointsof each of the multiple conductors 2 a, 2 b, 2 c remain in a singleplane. The tip holder 18 may also include one or more vacuum channels 25extending from the downstream end of the tip holder 18 to a vacuumconnection point located in the side of the tip holder 18.

The downstream end of the tip holder 18 may be in contact with aninsulator-applicator tip 20. The exterior surface of the insulatorapplicator tip 20 may be configured to guide molten insulator material12 into a circular shape around the multiple conductors 2 a, 2 b, 2 c.As a non-limiting example, the exterior surface of theinsulator-applicator tip 20 may have a round cross-section. In variousembodiments, at least a portion of the exterior surface of theinsulator-applicator tip 20 may be substantially frustoconical in shape,such that molten insulator material 12 is guided from a large diameterfirst end of the insulator-applicator tip 20 to a small diameter secondend of the insulator-applicator tip.

The interior surface of the insulator-applicator tip 20 is configured toaccept input through the guide channel 19 and the one or more vacuumchannels 25. As a non-limiting example, at least a portion of theinterior surface of insulator-applicator tip 20 may be at least in partfrustoconical in shape, and the second end of the insulator-applicatortip may comprise an exit channel configured to guide the multipleconductors 2 a, 2 b, 2 c through the extrusion head 4. In variousembodiments, the exit channel may have at least substantially the sameshape as the guide channel 19, such that the orientation of the multipleconductors 2 a, 2 b, 2 c is maintained throughout the extrusion head.

In various embodiments, an insulator material guide (not shown) may beprovided near the first end of the insulator-applicator tip 20. Theinsulator material guide may be configured to direct the molteninsulator material 12 onto the exterior surface of theinsulator-applicator tip 20 such that an at least substantially uniformflow rate of molten insulator material is provided around the entirecircumference of the exterior surface of the insulator-applicator tip.

As installed in the extruder head 4, the second end of theinsulator-applicator tip 20 may reside within a first interior portionof an isolator tip 21, the first interior portion of the isolator tipbeing located on the upstream side of the isolator tip. The exteriorsurface of the insulator-applicator tip 20 may be spaced away from thefirst interior surface of the isolator tip 21, such that an insulatorchannel 22 is formed therebetween.

A second interior portion of the isolator tip 21, located at thedownstream side of the isolator tip, may be spaced apart from anexterior surface of a secondary tip 23. In various embodiments, apolyamide channel 24 is formed between the second interior surface ofthe isolator tip 21 and the exterior surface of the secondary tip 23. Asillustrated in FIG. 2, the direction of flow of the polyamide 6 (or acombination of polyamide 6 and additive composition 9) along thepolyamide channel 24 may be at least partially opposite the direction offlow of the multiple conductors 2 a, 2 b, 2 c. Therefore, in variousembodiments, the second interior surface of the isolator tip 21 mayinclude a redirection portion configured to redirect the moltenpolyamide into the direction of travel of the multiple conductors 2 a, 2b, 2 c. In various embodiments, a polyamide guide (not shown) may beprovided near an entrance to the polyamide channel 24. The polyamideguide may be configured to direct the molten polyamide 6 into thepolyamide channel 24 such that an at least substantially uniform flowrate of molten polyamide (or combination of polyamide 6 and additivecomposition 9) is provided around the entire circumference of theexterior surface of the secondary tip.

In various embodiments, the extruder head 4 may additionally comprise aheat sink 30 positioned between the insulator channel 22 and polyamidechannel 24. Because the polyamide 6 (or combination of polyamide 6 andadditive composition 9) may be extruded at a temperature higher than theextrusion temperature of the insulator material 12, the heat sink 30 isconfigured to prevent the extruder head 4 components adjacent to theinsulator material channel 22 from reaching a temperature substantiallyhigher than the insulator material extrusion temperature. In variousembodiments, the heat sink 30 may be provided as a metallic ringpositioned within a slot formed in the exterior of the isolator tip 21.The metallic material may be different from the material of theremaining components of the extruder head 4 and have high thermalconductivity. As a non-limiting example, the heat sink 30 may comprise acopper material. The heat sink 30 may, in various embodiments, beconfigured to conduct heat away from the extrusion head 4 and into asecond heat sink (not shown) positioned external to the extruder head 4.

Although the various components of the extruder head 4 are illustratedand described herein as having an interior surface and an exteriorsurface, such terms should not be construed as limiting. As will beunderstood by those skilled in the art, various embodiments may havealternative orientations. As a non-limiting example, at least one of theinsulator channel 22 and the polyamide channel 24 may be oriented suchthat the respective material flows may be in a direction substantiallydifferent from that described herein, with respect to the direction offlow of the multiple conductors 2 a, 2 b, 2 c.

Extrusion Process

Referring now to FIGS. 2, 2A-A and 2B-B, which illustrate a coextrusionprocess for extruding an outer sheath layer onto the multiple conductors2 a, 2 b, 2 c, a process for producing an electrical cable according tovarious embodiments of the present invention will now be described. Suchprocess may be performed continuously, such that a long cable having atleast substantially uniform physical properties along the entire lengthof the cable may be produced. Although FIG. 2 illustrates a coextrusionprocess, as will be understood by those skilled in the art, a tandemextrusion process may also be used to produce an electrical cable. Invarious embodiments, the multiple conductors 2 a, 2 b, 2 c may be fedinto an upstream end of the extruder head 4, and into a tip holder 18.When being fed into the upstream end of the extruder head 4, themultiple conductors 2 a, 2 b, 2 c may be in a nominally flatconfiguration, such that a center point of each of the multipleconductors 2 a, 2 b, 2 c are aligned within a single plane. In variousembodiments, the multiple conductors 2 a, 2 b, 2 c may be fed throughthe guide channel 19 extending along the length of the tip holder 18.

Upon exiting the tip holder 18, the multiple conductors 2 a, 2 b, 2 cmay enter an interior portion of an insulator-applicator tip 20. Molteninsulator material 12 is concurrently fed through the insulator channel22 at a rate such that the insulator material 12 forms a first sheathlayer 27 having an at least substantially circular cross section and auniform, predefined thickness at substantially the same rate that themultiple conductors 2 a, 2 b, 2 c are fed into the extruder head 4. Inpreferred embodiments, PVC, heated to a temperature of at least 350degrees Fahrenheit, may be fed through the insulator channel 22 andextruded using a tube extrusion method around the multiple conductors 2a, 2 b, 2 c to form a first sheath layer 27. In various embodiments, thefirst sheath layer 27 may have an at least substantially circular crosssection surrounding the multiple conductors 2 a, 2 b, 2 c.

As the multiple conductors 2 a, 2 b, 2 c and first sheath layer 27 arefed into the secondary tip 23, polyamide 6 is concurrently fed throughthe polyamide channel 24 and onto the surface of the first sheath layer27, thus forming a second sheath layer 26 thereon. In variousembodiments, the polyamide 6 may be combined with an additivecomposition 9 prior to introduction into the extruder head 4, such thatthe mixture is extruded to form the second sheath layer 26. Thepolyamide 6 and additive composition 9 may be fed through the polyamidechannel 24 at a rate such that the polyamide and additive compositionmixture forms a second sheath layer 26 having a predefined thickness atsubstantially the same rate that the multiple conductors 2 a, 2 b, 2 care fed into the extruder head 4. In preferred embodiments, polyamide 6may be heated to a temperature of at least 500 degrees Fahrenheit andfed through the polyamide channel 24 and extruded onto the exteriorsurface of the first sheath layer 27 to form the second sheath layer 26.The molten polyamide 6 is extruded onto the surface of the first sheathlayer 27, and as the first sheath layer and the polyamide 6 cool, theymay mechanically bond together. The resulting combination of the firstsheath layer 27 and second sheath layer 26 may have an at leastsubstantially circular cross section surrounding the multiple conductors2 a, 2 b, 2 c.

The molten polyamide 6 (or combination of polyamide 6 and additivecomposition 9) may have a low viscosity at the polyamide extrusiontemperature. As a predictable, uniform flow rate of molten polyamidearound the perimeter of an oval die slot could not be achieved usingconventional polyamide extrusion parameters. As a non-limiting example,extruding molten polyamide through a non-circular extrusion die exit toform a second sheath layer 26 may cause an uneven flow rate in themolten polyamide around the perimeter of the extrusion die and thuscause an uneven flow rate in the extrusion direction. Therefore, theresulting second sheath layer 26 may have an inconsistent (non-uniform)thickness around the perimeter of the second sheath layer. However,utilizing an extruder head 4 incorporating a polyamide channel 24 havinga circular exit facilitates a uniform flow rate around the perimeter ofthe circular exit, and the resulting second sheath layer 26 thereforehas an at least substantially uniform thickness around the perimeter ofthe second sheath layer.

As the multiple conductors 2 a, 2 b, 2 c, the first sheath layer 27, andthe second sheath layer 26 exit the secondary tip 23, the combination ofthe first sheath layer 27 and second sheath layer 26 maintains an atleast substantially circular cross section with a uniform thickness,while the multiple conductors 2 a, 2 b, 2 c maintain a nominally flatorientation. A cross section showing the relative configurations of themultiple conductors 2 a, 2 b, 2 c, the first sheath layer 27, and thesecond sheath layer 26 are shown in FIG. 2A-A. As illustrated in FIG.2A-A, the first sheath layer 27 and second sheath layer 26 each have auniform thickness around the perimeter of the cross section.

While the multiple conductors 2 a, 2 b, 2 c are fed through the extruderhead 4, a negative pressure is applied through the one or more vacuumchannels 25 located within the tip holder 18. The negative pressure maybe applied in the form of a vacuum, and may be configured such that thecombined first sheath layer 27 and second sheath layer 26 are pulledonto the surface of the multiple conductors 2 a, 2 b, 2 c at somedistance downstream from the exit of the polyamide channel 24. FIG. 2B-Bshows a cross sectional view of an exemplary resulting cable 13, whereinthe outer sheath layer has a stadium shape surrounding the multipleconductors 2 a, 2 b, 2 c. As illustrated in FIG. 2B-B, the first sheathlayer 27 and second sheath layer 26 of the resulting cable 13 each havea uniform thickness around the perimeter of the cable. A cutaway view ofthe resulting cable 13 according to various embodiments is shown in FIG.3A.

Although not illustrated in FIG. 1 or FIG. 2, a dam paper 28 may be fedthrough the extruder head 4 with the multiple conductors 2 a, 2 b, 2 c.As will be understood by those skilled in the art, the dam paper 28 maybe folded around the multiple conductors 2 a, 2 b, 2 c, prior to themultiple conductors entering the tip holder 18. Moreover, at least oneconductor 2 b may be individually enclosed in a paper barrier 29 priorto being introduced to the extruder head 4. As will be understood bythose skilled in the art, the paper barrier 29 may be folded around theat least one conductor 2 b prior to the at least one conductor enteringthe extruder head 4.

Non-Circular Electrical Cable Having a Reduced Pull Force

The resulting cable 13 produced according to the above described methodswill now be described with reference to FIG. 3. Referring now to FIG. 3,the multiple conductors 2 a, 2 b, 2 c, may be loosely enclosed within adam paper 28 in a nominally flat orientation, and thus the resultingcable 13 may have a nominally flat shape. Although surrounding themultiple conductors 2 a, 2 b, 2 c such that the dam paper 28 is incontact with the surface of each of the multiple conductors, the dampaper may not be mechanically bonded to the multiple conductors. Thecombination of the multiple conductors 2 a, 2 b, 2 c and dam paper 28are enclosed in the outer sheath comprising the first sheath layer 27and the second sheath layer 26. As described herein, the exteriorsurface of the first sheath layer 27 may be mechanically bonded to theinterior surface of the second sheath layer 26. In various embodiments,the mechanical bond between the first sheath layer 27 and the secondsheath layer 26 may be a heat bond that may be formed as the moltenpolyamide 6 is extruded onto the surface of the first sheath layer 27.The outer sheath may be in contact with the dam paper 28, although theouter sheath may not be mechanically bonded thereto, such that the outersheath may loosely enclose the dam paper 28 and multiple conductors 2 a,2 b, 2 c while having a nominally flat cross section corresponding tothe nominally flat orientation of the multiple conductors 2 a, 2 b, 2 c.As a non-limiting example, where the multiple conductors 2 a, 2 b, 2 care arranged such that the center points of each of the multipleconductors are within a single plane, the outer sheath may have astadium-shape or flat oval cross section. Moreover, in variousembodiments, a bare conductor 2 b may be individually enclosed in apaper barrier 29. In various embodiments, the resulting cable does notcomprise a dam paper 28, such that the interior surface of the firstsheath layer 27 may be in contact with the exterior surface of themultiple conductors 2 a, 2 b, 2 c. In such configurations, the firstsheath layer 27 may not be mechanically bonded to the exterior surfaceof the multiple conductors 2 a, 2 b, 2 c.

In various embodiments, each of the first sheath layer 27 and secondsheath layer 26 may have a substantially uniform thickness around theperimeter of the cable (see FIG. 2B-B). For example, the thickness ofthe second sheath layer 26 may have a 40% tolerance, and more preferablya 20% tolerance, and even more preferably a 17% tolerance. In variousembodiments, such a tolerance may correspond to a 2 mil tolerance, andmore preferably a 1 mil tolerance around the perimeter of the cable 13.For example, such a tolerance may correspond to a second sheath layerthickness of 6 mils+/−1 mil or 6 mils+/−0.5 mils. As yet othernon-limiting examples, such a tolerance may correspond to a secondsheath layer thickness of 4 mils+/−1 mil or a second sheath layerthickness of 5 mils+/−1 mil. Similarly, the thickness of the firstsheath layer 27 may have a 10% tolerance, and more preferably an 8.25%tolerance. Such a tolerance may correspond to a first sheath layerthickness of 24 mils+/−0.5 mils or a first sheath layer thickness of 24mils+/−1 mil.

The overall thickness of the combination of the outer sheath and dampaper 28 (if included) may be sufficient to satisfy applicableregulatory requirements or standards established by industry groups(e.g., the Underwriters Laboratory) or other reviewing entities.Alternatively, the outer sheath alone may have a thickness sufficient tosatisfy applicable regulatory requirements or standards. As anon-limiting example, the overall thickness of the combination of theouter sheath and the dam paper 28 may be at least 30 mils. Specifically,the second barrier layer 26 may have a thickness between 5-8 mil, butpreferably 6 mil, the first barrier layer 27 may have a thicknessbetween 23-25 mil, but preferably 24 mil, and the dam paper 28 may havea thickness of 4 mil. Moreover, as illustrated in detail below, thesecond sheath layer 26 may have a low dynamic coefficient of friction,and thus a low pulling force is necessary for installation of the cable13 in an installation site.

Pulling Force Test Apparatus, Methods, and Results

FIGS. 4A and 4B illustrate various components of a pull-force testapparatus that was used to determine the effects on necessary pullingforce of incorporating a second sheath layer 26 as described herein intoa cable. As illustrated in FIG. 4A, the test apparatus comprises twoidentical test walls 100 each comprising a 90° corner 101, aligned toform a “U” shape. Each test wall 100 comprises a short wall section 102and a long wall section 103 adjacent the corner 101. The short wallsection comprises 4 vertical studs 110, and the long wall sectioncomprises 7 vertical studs 110. Each of the studs 110 is supported by asupport structure comprising a base 121, a top plate 122 and a soleplate 123 collectively configured to maintain the spacing andorientation of the studs 110 relative to one another.

Each stud 110 comprises a 1½″ by 3½″ soft pine board, commonly referredto as a “2×4.” The studs 110 are spaced on 16-inch centers (i.e., spacedsuch that a 16″ long space exists between the centerline of each stud),and aligned such that the wide-sides (i.e., 3½″ sides) of adjacent studs110 are in parallel planes. Each stud has a 10″ tall by 1″ wide, stadiumshaped test slot 111 extending therethrough in a direction perpendicularto the orientation of the 3½″ side of the stud 110. The verticalcenterline of the slot is aligned with the vertical centerline of eachcorresponding stud 110.

The studs 110 are each configured to support a pulling block 115 asillustrated in FIG. 4B. Each pulling block comprises a 1½″ by 3½″ softpine board having five, ¾″ diameter test holes 116A-116E extendingtherethrough in a direction perpendicular to the orientation of the 3½″side of the pulling block 115. The test holes 116A-116E are arranged on2″ centers (e.g., spaced such that a 2″ long space exists between thecenter point of each test hole) and aligned such that the centerline ofthe 3½ inch side of the pulling block 115 extends through the centerpoint of all five test holes 116A-116E. Moreover, the center point ofthe center test hole 116C is concentric with the center point of the 3½inch side of the pulling block 115.

When mounted on a stud 110, the center point of the center test hole116C of the pulling blocks 115 is concentric with the center point ofthe test slot 111 of the stud 110. In the illustrated embodiment ofFIGS. 4A and 4B, the pulling blocks 115 are each attached to acorresponding stud 110 using bolts secured through correspondingmounting holes of the pulling blocks 115 and studs 110. For each section102, 103 of the test wall 100, the pulling blocks 115 are mounted to thestuds such that the pulling blocks 115 are spaced on 16″ centers (i.e.,the pulling blocks 115 each have the same orientation relative to thecorresponding studs 110 in relation to the corner 101). Moreover, thepulling blocks 115 are mounted to corresponding studs 110 such that eachpulling block 115 is closer to the corner 101 than the correspondingstud 110. In such orientation, the pulling blocks 115 nearest to thecorner 101 on each section 102, 103 are adjacent.

The two test walls 100 are arranged in a “U” shape, such that the shortsection 102 of a first test wall 100 is parallel with the long section103 of a second test wall 100, and the long section 103 of the firsttest wall 100 is proximate the short section 102 of the second test wall100. As arranged, the long section 103 of the first test wall 100 andthe short section 102 of the second test wall 100 collectively form an11-stud wall section. The stud 1101 e forming the end of the longsection 103 of the first test wall 100 is spaced apart from the stud 110se forming the end of the short section 102 of the second test wall 100such that the pulling blocks 115 associated with the studs 1101 e, 110se are arranged on a 16″ center.

A section of cable to be tested is threaded through test holes inadjacent pulling blocks 115 through the entire “U”-shaped testapparatus. FIG. 4C is a schematic diagram of a short section 102 of atest wall 100 illustrating how a cable 13 is threaded through the testapparatus. As shown in FIG. 4C, the cable 13 is threaded throughalternating test holes 116A-B. In the illustrated example, the cable 13is threaded through a top-level test hole 116A of a first pulling block115, then a second-level test hole 116B of a second, adjacent pullingblock 115, then a top-level test hole 116A of a third, adjacent pullingblock 115. This alternating threading pattern is repeated over theentirety of the test apparatus. FIG. 4C illustrates only a subsection ofthe entirety of the test apparatus, however the same alternatingthreading pattern shown in FIG. 4C is repeated throughout the entiretest apparatus. The cable 13 is threaded through a pattern ofadjacent-level test holes, however any threading pattern utilizingadjacent pattern test holes may be used. As illustrated, the cable maybe threaded through holes 116A and 116B, although the cable mayalternatively be threaded through holes 116B and 116C; holes 116C and116D; or holes 116D and 116E. During testing, each test hole is utilizedfor a single test before the pulling blocks 115 are discarded andreplaced.

The cable 13 is pulled through the test apparatus in a test directionfrom an entrance side to an exit side. A length of cable at least equalin length to the length of cable to be tested is unspooled on theentrance side, such that any increased pulling force attributable to thecable being removed from the spool is minimized. The cable extendingbeyond the exit side of the test apparatus is secured to a 500-lb loadcell (e.g., a Smart S-beam parallel/shear beam load cell), which issecured via a rope to a cable tugger (not shown) located 12 feet awayfrom the exit end of the test apparatus and oriented such that the cable13 is pulled at least substantially horizontally between the exit sideof the test apparatus and the cable tugger. The load cell is inelectrical communication with a data recording device (e.g., a computingdevice) configured to record the amount of force measured by theload-cell. Other load cells, such as a 20-lb Smart S-beam parallel/shearbeam load cell, may also be used in the test.

During testing, the cable tugger applies a pulling force to the cable 13sufficient to pull the cable through the testing apparatus at a uniformrate until a 10-foot long length of cable 13 has been pulled through thetest apparatus. The load cell measures the amount of pulling forceapplied by the cable tugger, and communicates the data to the datarecording device. For each test sample type, 3 samples were tested bypulling a 10-foot long length of cable 13 through the test apparatususing the same set of holes in the pulling blocks 115. Using the sameset of holes in the pulling blocks 115 substantially recreates theeffect of pulling a single long test sample through the testingapparatus. Thus, as additional test samples are pulled through the holesin the pulling blocks 115, the pulling force necessary to pull thesample through the test apparatus decreases. This decrease in necessarypulling force may be attributable to a smoothing of the interior of theholes of the pulling blocks 115 as cable is pulled across the surfacesof the holes, or it may be attributable to residual lubricant beingdeposited on the surface of the holes of the pulling blocks 115. Theamount of force measured by the load cell during each measurement pointof the 3 tests for each sample type is averaged to determine an averagepulling force necessary to pull the cable through the test apparatus.

The pull test was performed on several 12/2 NM-B cable samples includingcables marketed by various companies, cables produced without a secondsheath layer 26 as discussed herein, and cables having various levels ofadditives incorporated into the sheath layer 26. The results of the pulltest are summarized in Table 1. These results illustrate that a cablehaving a second sheath layer 26 as discussed herein requiressignificantly less pulling-force to install than similar NM-B cablesthat do not have a second sheath layer 26.

TABLE 1 Measured Average Pulling Sample Type Force (lb.) Company 1“12/2” cable without a second sheath 36.3 layer Company 2 “12/2” cablewithout a second sheath 64.5 layer Company 3 “12/2” cable without asecond sheath 48.0 layer “12/2” Test Sample 1 having a nylon second 19.0sheath layer without flame retardant additive and with 12% compositionof silicon lubricant “12/2” Test Sample 2 having a nylon second 18.0sheath layer with 5% composition of flame retardant additive and with12% composition of silicon lubricant “12/2” Test Sample 3 having a nylonsecond 17.5 sheath layer with a 10% composition of flame retardantadditive and with 12% composition of silicon lubricant

As shown in Table 1, the test samples having a nylon second sheath layerrequired at least 48% less pulling force than the nearest comparablecable to pull the cable through the test apparatus.

CONCLUSION

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

That which is claimed:
 1. A non-circular electrical cable comprising:one or more conductors arranged in a non-circular arrangement, whereinthe one or more conductors comprises a first conductor, a secondconductor and a ground wire, wherein the first conductor has a firstinsulative coating on an external surface of the first conductor and thesecond conductor has a second insulative coating on an external surfaceof the second conductor, and wherein the first conductor, secondconductor, and ground wire are arranged in a nominally flatconfiguration; and an exterior sheath surrounding the conductors havinga non-circular cross-section, the exterior sheath consisting of a firstsheath layer and an extruded second sheath layer, wherein: the firstsheath layer has an exterior surface and an interior surface, whereinthe interior surface of the first sheath layer has a non-circular crosssection and surrounds the one or more conductors, and wherein the firstsheath layer comprises a plastic material; and the extruded secondsheath layer has an exterior surface and an interior surface, whereinthe second sheath layer comprises a polyamide and the interior surfaceof the extruded second sheath layer is bonded with the exterior surfaceof the first sheath layer.
 2. The non-circular electrical cable of claim1, wherein the polyamide is a nylon material.
 3. The non-circularelectrical cable of claim 2, wherein the second sheath layer has auniform thickness measured between the exterior surface and the interiorsurface of the second sheath layer, and that the thickness varies by nomore than 10%.
 4. The non-circular electrical cable of claim 2, whereinthe non-circular electrical cable has a reduced required pulling forcerequired for installation, wherein the reduced required pulling force isno more than about 50% of the force required to install a cable lackingthe second sheath layer.
 5. The non-circular electrical cable of claim1, wherein the second sheath layer additionally comprises a lubricantfor decreasing the pulling force of the non-circular electrical cable.6. The non-circular electrical cable of claim 5, wherein the lubricantcomprises a silicon-based lubricant.
 7. The non-circular electricalcable of claim 5, wherein the lubricant is homogenously distributedwithin the second sheath layer.
 8. The non-circular electrical cable ofclaim 1, wherein the first sheath layer comprises a poly-vinyl chloridematerial.
 9. The non-circular electrical cable of claim 8, wherein thefirst sheath layer comprises a foamed poly-vinyl chloride material. 10.The non-circular electrical cable of claim 8, wherein the first sheathlayer comprises a re-grind poly-vinyl chloride material.
 11. Thenon-circular electrical cable of claim 1, wherein the exterior sheathhas a nominally flat cross-section.
 12. A non-circular electrical cablecomprising: one or more conductors arranged in a non-circulararrangement; and an exterior sheath surrounding the conductors having anon-circular cross-section, the exterior sheath consisting of a firstsheath layer and an extruded second sheath layer, wherein the exteriorsheath defines an interior volume surrounded by the interior surface ofthe first sheath layer, and wherein the non-circular electrical cablefurther comprises a paper positioned within the interior volume andadjacent the interior surface of the first sheath layer, and wherein:the first sheath layer has an exterior surface and an interior surface,wherein the interior surface of the first sheath layer has anon-circular cross section and surrounds the one or more conductors, andwherein the first sheath layer comprises a plastic material; and theextruded second sheath layer has an exterior surface and an interiorsurface, wherein the second sheath layer comprises a polyamide and theinterior surface of the extruded second sheath layer is bonded with theexterior surface of the first sheath layer.
 13. The non-circularelectrical cable of claim 12, wherein the first sheath layer and secondsheath layer are mechanically bonded and the first sheath layer looselysurrounds the paper.
 14. A non-circular electrical cable comprising: oneor more conductors arranged in a non-circular arrangement; and anexterior sheath loosely surrounding the one or more conductors andhaving a non-circular cross-section, the exterior sheath consisting of afirst sheath layer and an extruded second sheath layer, wherein: thefirst sheath layer has an exterior surface and an interior surface,wherein the interior surface of the first sheath layer has anon-circular cross section and surrounds the one or more conductors, andwherein the first sheath layer comprises a plastic material; and theextruded second sheath layer has an exterior surface and an interiorsurface, wherein the second sheath layer comprises a polyamide and theinterior surface of the extruded second sheath layer is mechanicallybonded with the exterior surface of the first sheath layer.
 15. Thenon-circular electrical cable of claim 14, wherein the mechanical bondcomprises a heat bond.
 16. A non-circular electrical cable comprising:one or more conductors arranged in a non-circular arrangement; and anexterior sheath surrounding the conductors having a non-circularcross-section, wherein the exterior sheath has an at least substantiallyuniform thickness measured between an interior surface of the exteriorsheath and an exterior surface of the exterior sheath and the exteriorsheath comprises a first sheath layer and an extruded second sheathlayer, wherein: the first sheath layer has an exterior surface and aninterior surface, wherein the interior surface of the first sheath layerhas a non-circular cross section and surrounds the one or moreconductors, and wherein the first sheath layer comprises a plasticmaterial; and the extruded second sheath layer has an exterior surfaceand an interior surface, wherein the second sheath layer comprises apolyamide and the interior surface of the extruded second sheath layeris bonded with the exterior surface of the first sheath layer, andwherein the extruded second sheath layer has a thickness measuredbetween the exterior surface of the extruded second sheath layer and theinterior surface of the extruded second sheath layer of between about3-7 mils.
 17. The non-circular electrical cable of claim 16, wherein theexterior sheath has an at least substantially uniform thickness ofbetween about 26-32 mils.